Many products relating to optical disks have appeared on the market in recent years. In addition to the spread of compact disk players for domestic and personal use, reduction of a price of a compatible player being capable of playing a plural kinds of optical disks such as a laser disk, a compact disk and the like accelerates the spread of such the products. With respect to soft ware, soft war having a good quality and a low price appear, being going to take a leading part in a field of AV (audio visual), comparable to video. On the other hand, the optical disk is applied to a field of computer as a ROM (a read only memory), utilizing its large storage capacity and high accessibility. The use of the optical disk will widely expand in future by reason of the spread of an optical disk of a direct-read-after-write type which can be overwritten.
Data of the optical disk are typically arranged spirally from an inner periphery to an outer periphery of the disk as pits and the data are determined depending on presence of the pit. A role of the optical servo is to focus rays of light emitted from an optical system onto a predetermined array of the pits upon reproduction of data of the optical disk to bring the data into a readable state. The optical servo is classified into a focus servo which serves to focus the optical system onto a surface of an optical disk and a tracking servo which positions beams for reproducing information onto an array of pits on a surface of an optical disk.
There is a conventional optical disk system (Japanese Patent Application No. SHO 63-293614, Application Date; May 27, 1987, Title of the Invention; Position Controlling System).
In the conventional optical disk system, error signals are processed by a digital filter, then rounded to eight bits to be used as driving data. Lower-order data are lost because of the rounding.
The conventional optical system, therefore, has a problem that it is difficult to ensure sufficient accuracy in the system since the driving data are rounded to eight bits.
An object of the present invention is to overcome the above problem and to provide an optical disk system having a good control characteristic.